http://www.biology.arizona.edu/biomath/tutorials/Notation/SetBuilderNotation.html

For your problem…

domain: ( – ∞, 1) ∪ (1, 4) ∪ (4, + ∞)

You use the union symbol (∪) between these three intervals because we are removing points x = 1 and x = 4.

The parentheses ( ) mean “not including” ; you change them to brackets [ ] if the numbers inside them are “included” in your domain.

Example, for {x/ x is an element of all real numbers, x > or equal to 1 and x < or equal to 5}, it's simply [1,5] . For {x/ x is an element of all real numbers, x > or equal to 1 and x not = to 5}, it’s simply [1, 5) (5, +infinity) .

*though for infinity you have to use the symbol, not the word, and also for infinity, you always have to write a parenthesis, never a bracket.

Basic math, kiddo.